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fix(physics): stop forceAtlas2Based layout from rotating forever (#2193) #2450

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8e49c86
fix(physics): stop forceAtlas2Based layout from rotating forever (#2193)
bojanstef Jun 19, 2026
a7796e0
test(physics): regenerate forceAtlas2Based snapshots for the rotation…
bojanstef Jun 19, 2026
91b1da4
fix(physics): apply forceAtlas2 degree weighting symmetrically (#2193)
bojanstef Jun 20, 2026
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164 changes: 82 additions & 82 deletions __snapshots__/test/snapshots.test.ts.js
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -193,12 +193,12 @@ exports['Physics snapshots Barnes Hut defaults binary tree 1'] = {

exports['Physics snapshots Force Atlas 2 defaults 2 connected nodes 1'] = {
"1": {
"x": -11,
"y": 58
"x": -14,
"y": 64
},
"2": {
"x": -8,
"y": -68
"x": -10,
"y": -74
}
}

Expand All @@ -215,172 +215,172 @@ exports['Physics snapshots Force Atlas 2 defaults 2 disconnected nodes 1'] = {

exports['Physics snapshots Force Atlas 2 defaults 2 doubly connected nodes 1'] = {
"1": {
"x": -18,
"y": 64
"x": -16,
"y": 71
},
"2": {
"x": 3,
"y": -65
"x": 0,
"y": -73
}
}

exports['Physics snapshots Force Atlas 2 defaults 6 node circle 1'] = {
"1": {
"x": -23,
"y": -151
"x": -31,
"y": -191
},
"2": {
"x": -133,
"y": -48
"x": -173,
"y": -61
},
"3": {
"x": -111,
"y": 102
"x": -141,
"y": 129
},
"4": {
"x": 34,
"y": 147
"x": 41,
"y": 187
},
"5": {
"x": 145,
"y": 45
"x": 184,
"y": 58
},
"6": {
"x": 120,
"y": -104
"x": 151,
"y": -131
}
}

exports['Physics snapshots Force Atlas 2 defaults 6 node complete graph 1'] = {
"1": {
"x": -160,
"y": -106
"x": -211,
"y": -144
},
"2": {
"x": -171,
"y": 94
"x": -234,
"y": 117
},
"3": {
"x": 175,
"y": 84
"x": 220,
"y": 137
},
"4": {
"x": 11,
"y": 197
"x": -8,
"y": 264
},
"5": {
"x": 39,
"y": -151
"x": 22,
"y": -247
},
"6": {
"x": 110,
"y": -109
"x": 220,
"y": -116
}
}

exports['Physics snapshots Force Atlas 2 defaults 6 node star 1'] = {
"1": {
"x": 12,
"y": -2
"x": 9,
"y": -1
},
"2": {
"x": -146,
"y": -12
"x": -196,
"y": -16
},
"3": {
"x": -40,
"y": -150
"x": -51,
"y": -197
},
"4": {
"x": 154,
"y": -73
"x": 193,
"y": -97
},
"5": {
"x": 121,
"y": 116
"x": 155,
"y": 145
},
"6": {
"x": -48,
"y": 146
"x": -68,
"y": 192
}
}

exports['Physics snapshots Force Atlas 2 defaults binary tree 1'] = {
"1": {
"x": 52,
"y": 48
"x": 73,
"y": 104
},
"2": {
"x": -97,
"y": 87
"x": -129,
"y": 123
},
"3": {
"x": 206,
"y": 34
"x": 269,
"y": 41
},
"4": {
"x": -113,
"y": -86
"x": -166,
"y": -124
},
"5": {
"x": -135,
"y": 245
"x": -202,
"y": 345
},
"6": {
"x": 211,
"y": -132
"x": 327,
"y": -187
},
"7": {
"x": 199,
"y": 204
"x": 312,
"y": 276
},
"8": {
"x": -278,
"y": -65
"x": -396,
"y": -106
},
"9": {
"x": -26,
"y": -228
"x": -61,
"y": -342
},
"10": {
"x": -279,
"y": 227
"x": -382,
"y": 329
},
"11": {
"x": -49,
"y": 358
"x": -86,
"y": 488
},
"12": {
"x": 356,
"y": -104
"x": 501,
"y": -161
},
"13": {
"x": 213,
"y": -277
"x": 296,
"y": -368
},
"14": {
"x": 340,
"y": 156
"x": 484,
"y": 221
},
"15": {
"x": 134,
"y": 333
"x": 215,
"y": 439
},
"16": {
"x": -304,
"y": -209
"x": -437,
"y": -282
},
"17": {
"x": -360,
"y": 55
"x": -499,
"y": 49
},
"18": {
"x": 63,
"y": -344
"x": 81,
"y": -461
},
"19": {
"x": -138,
"y": -327
"x": -182,
"y": -474
}
}

Expand Down
62 changes: 57 additions & 5 deletions lib/network/modules/components/physics/FA2BasedRepulsionSolver.js
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,57 @@ class ForceAtlas2BasedRepulsionSolver extends BarnesHutSolver {
this._rng = Alea("FORCE ATLAS 2 BASED REPULSION SOLVER");
}

/**
* The repulsion "charge" of a node: its mass weighted by its degree
* (`edges.length + 1`). ForceAtlas2 scales repulsion by node degree so that
* highly interconnected hubs are pushed to the periphery.
*
* The degree must enter the force symmetrically. ForceAtlas2's repulsion is
* `k * (deg(a)+1) * (deg(b)+1) / distance` (Jacomy et al. 2014), i.e. it
* depends on the product of both degrees, so the force on `a` from `b` equals
* the force on `b` from `a` (Newton's third law). Applying the degree to only
* the receiving node — as was done previously — makes the pairwise force
* non-reciprocal and injects a net torque every tick. Velocity damping caps
* but never removes it, so a converged layout spins about its center of mass
* forever (issue #2193). Folding the degree into the mass used both to build
* the Barnes-Hut tree and to evaluate the force keeps it reciprocal.
* @param {Node} node
* @returns {number} the degree-weighted mass of the node
* @private
*/
_getMass(node) {
return node.options.mass * (node.edges.length + 1);
}

/**
* Update the mass of a branch using the degree-weighted mass (see _getMass),
* so the accumulated branch mass and its center of mass are consistent with
* the degree-weighted repulsion applied in _calculateForces.
* @param {object} parentBranch
* @param {Node} node
* @private
*/
_updateBranchMass(parentBranch, node) {
const mass = this._getMass(node);
const centerOfMass = parentBranch.centerOfMass;
const totalMass = parentBranch.mass + mass;
const totalMassInv = 1 / totalMass;

centerOfMass.x = centerOfMass.x * parentBranch.mass + node.x * mass;
centerOfMass.x *= totalMassInv;

centerOfMass.y = centerOfMass.y * parentBranch.mass + node.y * mass;
centerOfMass.y *= totalMassInv;

parentBranch.mass = totalMass;
const biggestSize = Math.max(
Math.max(node.height, node.radius),
node.width,
);
parentBranch.maxWidth =
parentBranch.maxWidth < biggestSize ? biggestSize : parentBranch.maxWidth;
}

/**
* Calculate the forces based on the distance.
* @param {number} distance
Expand All @@ -38,14 +89,15 @@ class ForceAtlas2BasedRepulsionSolver extends BarnesHutSolver {
);
}

const degree = node.edges.length + 1;
// the dividing by the distance cubed instead of squared allows us to get the fx and fy components without sines and cosines
// it is shorthand for gravityforce with distance squared and fx = dx/distance * gravityForce
// dividing by the distance squared (rather than the cubed used by
// BarnesHutSolver) yields ForceAtlas2's linear 1/distance repulsion once the
// dx/dy components are factored in. Both parentBranch.mass and the node's
// mass are degree-weighted (see _getMass), so the repulsion is proportional
// to (degree+1) on both sides and stays reciprocal.
const gravityForce =
(this.options.gravitationalConstant *
parentBranch.mass *
node.options.mass *
degree) /
this._getMass(node)) /
Math.pow(distance, 2);
const fx = dx * gravityForce;
const fy = dy * gravityForce;
Expand Down
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